My guess on this has always been:- Money.
The cost of setting up a long haul route is enormous. Some items:
- Assess the route for capacity now and in the future - paperwork and research by clerical staff.
- Financial planning for aircraft, crew, fuel, supplies, marketing etc. Do you have spare a/c and crew or would you need to wet/dry lease for the first year?
- If considered viable then you have to commit to, say, one or two weekly rotations for, say, a summer season or a year.
- Then apply for the route and get slots.
- Set up the marketing and package deals with tour operators.
- Set up ground handling, fuel and supplies, maintenance and get credit and accounts for all that into place. This includes stop overs for crew at destination etc.
- Allocate a/c and staff, train staff for the route. Route proving flights which are non-revenue.
- Now market the route and hope someone buys a ticket ..!!
The above could easily take half a year and, in this day and age, the market could have changed. So you pick routes that you KNOW are going to work. Trying to find new city pairs and seasonal routes is better than going against an existing carrier, who has already spent all that money and can easily adjust their marketing price to retain the pax.
When the current recession/depression in the Western world is over, we might see new things but that is a minimum of five years away.